Epoxy resins are employed for a wide range of applications such as electronic components, electrical equipment, automotive parts, FRP, sporting equipment and so on, since the epoxy resins have better adhesiveness, better heat resistance and better moldability. Among them, flame-retardant agents, in particular brominated epoxy resins or antimony compounds are employed for copper-clad laminates and sealant that are employed for electronic components and electrical equipment. However, halogen-containing compounds or antimony compounds cause concerns about human safety, and therefore flame-retardant agents that have taken the environment into consideration are desired.
Conventionally, as the methods for adding flame-retardancy to epoxy resins, methods of kneading an additive-type flame-retardant agent to an epoxy resin, of modifying the epoxy resins by using a reactive flame-retardant agent whereby chemically reacting an epoxy resin and a flame-retardant agent, and so on, have been proposed.
Proposed methods of using an additive-type flame-retardant agent includes, for example: a method using alumina hydrate (Japanese Patent Application Laid-open No. H05-25369); a method of using modified red phosphorus (Japanese Patent Application Laid-open No. S63-156860); a method of using modified red phosphorus, alumina hydrate and silica powder (Japanese Patent Application Laid-open No. S58-198521) and so on.
However, using these additive-type flame-retardant agents may require larger amounts of the flame-retardant agents, thereby causing a problem of deterioration of the moldability of the compound material.
On the contrary, various methods of using reactive flame-retardant agents have been proposed since smaller amounts of flame-retardant agents are necessary.
For example, proposed methods includes: a method of using tris(hydroxypropyl)phosphine oxide (Japanese Patent Application Laid-open No. S57-195141), a method using phosphine oxide derivatives as represented by the following general formula (4):
(where x=0 to 2; y=1 to 3; and x+y=3; R represents methylene group or ethylene group) (Japanese Patent Application Laid-open No. S63-95223); a method of using organophosphorus compound as represented by the following general formula (5):
or the following general formula (6):
(where R is alkyl group-containing 1 to 6 carbons and n represents a number from 0 to 4) (Japanese Patent Application Laid-open No. H11-279258 and H11-166035); a method of using polyepoxy phosphonate compounds that is obtainable by reacting phosphonic acid with polyepoxy compounds having oxysilane group or epihalohydrin (Japanese Patent Application Laid-open No. S51-143620, H03-84025, H02-272014 and H02-269730) and so on.
Also, Japanese Patent Application Laid-open No. 2000-80251 discloses a method of using phosphorus-containing compounds having a general formula (7) of:
(where R′ is a compound including two or more phenolic OH; n is an integer number of 0 to 3; R″ is a linear or branched alkyl group having 1 to 8 carbons, cyclohexyl group, cyclopentyl group or aryl group, or alkyl-substituted or alkoxy-substituted alkyl group or aryl group having 1 to 18 carbons; wherein R″ may create a cyclic form with P atom; and m is 0 or 1).
Although various methods for adding flame-retardancy to epoxy resins with reactive flame-retardant agents have been proposed as described above, there are problems such as the difficulty in increasing phosphorus content in epoxy resins to a level where the flame-retardant effect is revealed or the difficulty in increasing flame-retardancy, or problems in which materials having phosphorus-oxygen bonds are inferior in moisture resistance and chemical resistance.
That is, an object of the present invention is to provide novel phosphorus-containing hydroquinone derivatives useful for reactive flame-retardant agents having phenolic hydroxyl group that reacts epoxy resins or epichlorohydrin and methods of producing them, and to provide phosphorus-containing epoxy resins produced by using the resultant phosphorus-containing hydroquinone derivatives, and further to provide flame-retardant epoxy resin compounds, sealant and laminates including phosphorus-containing epoxy resins and having improved flame-retardancy and chemical resistance.